Electric fuse



Dec. 17, 1940. v SUNDT 2,225,287

ELECTRIC FUSE Filed Jan. 20, 1959 "Zn denim":

Zfdzaard 1/. Saudi ax Patented Dec. 17, 1940 I UNITED STATES PATENTOFFICE 4 Claims.

This invention relates to improvements in electric fuses.

One object of the invention is to provide an improved fuse for use inelectric circuits such as those designed for carrying high voltage, lowamperage current and which may be employed satisfactorily in protectingdelicate electric instruments such as galvanometers, thermocouplers, orthe like. The improved fuse is adapted also for use in X-ray circuits,television circuits or other circuits employing electronic tubes.

A more specific object of the invention is to provide a fuse of theair-exhausted container type provided with lead wires, the inner ends ofwhich are bridged by a fusible element which is protected againstrupture during manufacture and subsequent use by means within thecontainer.

Another object of the invention is to provide a fuse of the typementioned having lead wires at opposite ends of the container forcarrying current through a fusible element and insulating meansinterconnecting the lead wires for protecting said element againsttensile stresses during manufacture.

A further object of the invention is to provide an air-evacuated orvacuum type fuse, the fusible .element and lead wires of which are sorelated as to minimize the danger of rupturing the element duringevacuation of the container and sealing thereof.

Other objects of the invention relate to features of construction andarrangement of parts which will be apparent from a consideration of thefollowing specification and accompanying drawing, wherein:

Fig. 1 is a side elevation of a fuse embodying the present improvements,the fuse being shown in position in a conventional fuse clip or holder;

Fig. 2 is a sectional view taken on line 2-2 of Fig. 1;

Fig. 3 is a detached perspective view of one of the two lead wires ofthe fuse; and

Fig. 4 is an elevation of the fuse illustrating end caps attached to thelead wires prior to the positioning of the caps on the ends of the fusecapsule or container.

In the drawing, l0 indicates a suitable container or capsule consisting,in the form shown, of a glass tube, the ends of which are openoriginally but in the completed fuse are sealed in contact with the leadwires which are indicated generally by the numerals ll, Ila. Since thefusible elements employed in low amperage fuses of the characterreferred to may be extremely delicate (depending on their intendedcurrent carrying capacity) and require careful handling to avoid ruptureduring attachment to the lead wires and installation of the assembly inthe container, the lead wires preferably are attached together rigidlyby a non-conducting member which is capable of withstanding the stressesimposed during handling.

In the embodiment of the invention illustrated, the intermediate portionof each of the lead wires is shown as bent or folded backwardly uponitself to provide an anchoring tang i2. The tangs of the pair of leadwires to be assembled in a container l0 are embedded in a non-conductor,such as a glass rod [3, the latter being fused to enable suchattachment. This member l3 secures the inner portions of the lead wirestogether rigidly and enables the same to be manipulated as a unit.

The free inner end portions of the lead wires extend laterally of theanchor 13 and terminate preferably in arcuate portions ll, the ends ofwhich portions are flattened as at l5, especially where the selectedfusible element is so delicate as to render attachment of the same tothe lead wires by soldering or welding either diflicult orimpracticable. In such instances, the fusible element I6 preferably iscemented to the inner ends of the wires, at the flattened areas thereof,by a conductive paste of any suitable composition known in the art. Suchpastes adhere to the flat areas more firmly than to the cylindricalsurface of the wire.

When the wires II, II a have been secured together by the anchoringmember i3 and the fusible element It attached to the areas I! asdescribed, the assembly is inserted in the tubular container in and oneend of the tube sealed around the wire II by fusion of the end of thetube in a flame in well known manner. The other end of the tube isheated and the wire Ila, instead of extending from the tube along theaxis thereof, is off-set from the axial center of the tube as shown,whereby the extreme adjacent end of the tube constitutes the tubulationor passage through which the air in the tube may be exhausted prior tosealing at the tip II. It has been found that by exhausting the air froman end of the container, the rush of air is less likely to fracture thedelicate fusible element than where the air is withdrawn through atubulation or air exhaust in the side of thetube as has been commonpractice heretofore.

The external portions of the lead wires ll, Ila are of sufficient lengthto enable the same be secured to the interiors of conducting end capsll. 'fhuathe ends of the wires preferably are soldered as at II to theinteriors of the caps after which suitable cement isinserted in the capsand the latter slipped over the adjacent ends of the container, the leadwires being gathered into the respective caps during the positioning ofthe latter on the ends of the container. The caps thus inclose not onlythe entire external portions of the lead wires but the sealing tips ofthe tube as well. The caps thus shield the tips against breakage, anddue to the internal attachment of the lead wires to the caps there is,compared with fuses where the wires are soldered to the exterior of thecaps, less likelihood of the wires becoming separated from the capsduring insertion of the fuses in conventional fuse clips I! or otherforms of fuse holders, such as extractor posts. In addition, thedescribed construction of the fuse avoids the relatively crude orunfinished appearance of air-exhausted fuses where the air is removedlaterally through tips intermediate the caps.

The inner end portions of the wires preferably extend into contact withthe inner wall of the tube at points opposite the anchoring orconnecting member 13 whereby independent vibrations of said ends andrelatively movement of the fuse assembly within the tube which would belikely to rupture the delicate fusible element ii, are inhibited. Byanchoring the tangs I! to the connecting member IS, the fuse assemblycan be inserted or drawn into position in the tube and the completion ofmanufacture of the fuse can be performed without imposing destructivestresses of the fusible element, as will be apparent. By-

carrying the lead wires out opposite ends of the tube as described, afuse construction adapted to carry high voltage is provided since thereis no danger of arcing between lead wires should the fuse blow as hasbeen the case in high voltage fuses of the type where both leadwires.enter the container at the same end. In such fuses, the voltagecapacity thereof is limited by the areover distance between the wireswhile with the present improvements, the adequate separation of the leadwires of the fuse assures the breaking of the circuit when the fusibleelement is destroyed by circuit over-load.

While I have shown and described a specific embodiment of the inventionfor the purpose of illustration, it will be apparent that changes may bemade therein without departing from the spirit of the invention. I

What I claim as new and desire to cover by Letters Patent is:

1. A fuse comprising a container, an assembly therein comprising a pairof lead wires sealed 'in the ends of the container, an insulating membercontacting the container and uniting said wires within the container atpoints remote from the inner ends of the wires, and a fusible elementbridging the ends of saidwires, said wires having container contactingportions intermediate said ends and said insulating member andcooperating with the latter for anchoring the assembly againsttransverse movement within the container.

2. A fuse comprising a container, an assembly therein comprising a pairof lead wires. an insulating member connecting said wires at pointsremote from the inner end portions thereof and arranged in longitudinalcontact with the wall of said container, said end portions being shapedfor contact with the wall of said container at points opposite saidinsulating member and cooperating with said insulating member forresisting lateral movement of the assembly within the container, and afusible element bridging said end portions of said wires.

3. A fuse comprising a tubular container, an assembly sealed thereincomprising a pair of lead wires, an insulating member connecting saidwires to prevent relative longitudinal movement of said wires within thecontainer and longitudinally contacting the wall of said container, saidwires being provided with portions extending into contact with thecontainer wall at points diametrically opposite said insulating memberand cooperating therewith for resisting lateral movement of the assemblywithin said container, and a fusible element connecting said wireswithin the container.

4. A fuse comprising a container, a pair of lead wires extending intothe same and each having an intermediate portion folded back upon itselfand terminating in a laterally off-set inner end, a fusible elementbridging the inner ends of said wires, and an insulating member withinthe container connected to said folded intermediate portions of saidwires.

EDWARD V. SUNDT.

